1. Field of the Invention
The present invention relates to heat fixing rolls having an improved outer layer of silicone rubber. The heat fixing rolls are used to fix images using dry electrophotographic toner powder by the application of heat and pressure. More specifically, the outer layer of the heat fixing roll can be made by continuous injection molding without a mold release agent, and the resulting heat fixing roll does not require impregnation with silicone oil to significantly increase the number of copies until offset.
2. Description of the Prior Art
The technique for fixing toner powder images which are transferred from a transfer drum onto a backing of paper by the dry electrophotographic process are well known. The method of fixing the toner powder image by pressure on the paper backing with a heated rubber roll, including a silicone rubber roll, is also well known.
Silicone rubber outer layer for the heat fixing rubber roll is well known. Heat curable silicone rubber crosslinked with an organic peroxide has been used to make heat fixing rolls as shown by Japanese Patent Publication No. Sho 36[1961]-1277 and Japanese Patent Publication No. Sho 54[1979]-159,485, published Dec. 17, 1979 and assigned to Showa Gum KK. However, such heat-curable silicone rubber has major drawbacks in terms of manufacturability: numerous kneading operations with double rolls are required because unvulcanized rubber is not sufficiently fluid, numerous manual operations are required because one must depend on winding steam molding or press molding as molding methods, and a continuous operation is impossible in the manufacturing process of the rolls. In addition, this type of silicone rubber has the drawback that secondary vulcanization is necessary in order to prevent the thermal decomposition phenomenon due to the decomposition products of organic peroxides, and post-molding polishing is required due to the use of winding steam vulcanization or press molding. Consequently, it is extremely disadvantageous in terms of manufacturability and production costs. Room temperature vulcanizable silicone rubber has also been used to make heat fixing rolls as shown by U.S. Pat. No. 4,074,001, issued Feb. 14, 1978 to K. Imai et al., and Japanese Patent Publication No. Sho 55[1980]-75,446, published June 6, 1980 and assigned to Tokyo Shibaura Electric Ltd., and Showa Electric Wire K.K. On the other hand, the room temperature-vulcanizable silicone rubber has the advantage that it is a liquid, but its manufacturability is markedly inferior because the cure time is extremely long, such as from several hours to several days. In addition, it also has such drawbacks as the fact that bumping of by-products is necessary because of the condensation reaction.
Aside from the above-mentioned drawbacks, with heat fixing rollers molded with heat-curable silicone rubber or room temperature-vulcanizable silicone rubber, even if compounded with or impregnated with silicone oil, the number of copies until offset is at best 30,000 to 50,000, and the industry strongly desires a further extension of this copy life, i.e., to increase the number of copies before the heat fixing roll expires.
Many types of silicone rubber compositions have been used to manufacture heat fixing rolls, but, because the outer layer demands certain characteristics, and because the outer layer can determine the copy life of the heat fixing roll, the compositions used to make this outer layer of silicone rubber have been well studied in an attempt to increase the copy life. Silicone rubber conventionally is made from compositions which contain fillers, especially reinforcing silica fillers, to improve their physical properties. The reinforcing silica fillers are added to improve the mechanical properties of the silicone rubber, namely the physical strength such as tensile strength. However, the presence of fillers, especially siliceous fillers, has been found to produce undesirable surface properties for heat fixing rolls.
Sanders et al. in U.S. Pat. No. 3,669,706, issued June 13, 1972, teach the undesirability of fillers conventionally used in silicone rubber compositions. Sanders et al. teach that fillers produce a ghost or offset image, especially reinforcing silica filler.
Donnelly et al. in U.S. Pat. No. 3,669,707, issued June 13, 1972, teach the undesirability of fillers, specifically high surface energy fillers such as silica, titanium oxide, and iron oxide. Donnelly et al. teach that silicone elastomer fuser blankets made from compositions containing 20 weight percent silica produce only 1000 copies before objectionable offset occurs and the blanket becomes useless. Also taught is that silicone elastomers which contain less than one weight percent reinforcing filler can provide 35,000 copies before failure occurs from mechanical breakdown of the elastomer. Donnelly et al. teach that low surface energy fillers, such as polytetrafluoroethylene, can produce in excess of 100,000 copies before offset or mechanical breakdown.
Murphy in U.S. Pat. No. 3,997,691, issued Dec. 14, 1976, teaches that silicone rubber containing fillers which release water can be used in amounts up to about 5.0 weight percent based on the weight of the silicone rubber or gum. Murphy teaches that silicone rubber containing 5 weight percent colloidal silica can be used to make fuser blankets if his method is used to fix the toner. At 5 weight percent colloidal silica, at least 11,500 copies were made before offset occurred.
Imai et al. in U.S. Pat. No. 4,074,001, issued Feb. 14, 1978, teach using a room temperature-vulcanizing silicone rubber composition for making fixing rolls. This silicone rubber composition contains silanol terminated diorganopolysiloxane, trialkylsilyl terminated diorganopolysiloxane of low viscosity, an alkoxysilane, a metal salt of an organic acid, and a filler mixture of calcium carbonate, iron oxide, and titanium oxide. Imai et al. teach that these compositions contain substantially no siliceous filler. Imai et al. have discovered an inorganic filler mixture which can be used in silicone rubber for fixing rolls, but specifically excludes siliceous fillers. Imai et al. do teach the use of silicone oil, the trialkylsilyl terminated diorganopolysiloxane, in their room temperature-vulcanizable silicone rubber.
Murphy in U.S. Pat. No. 4,126,722, issued Nov. 21, 1978, teaches that a silicone rubber composition containing benzoic acid and some silica can be used to make the outer layer of silicone rubber for heat fixing rolls. Murphy teaches in this patent that 8 parts by weight silica filler per 100 parts by weight siloxane reduces the number of copies from 80,000 to 70,000 before offset occurred compared to no silica filler. Murphy also teaches reducing the silica filler to 3 parts by weight can increase the number of copies up to 200,000 before offset occurs.
Matsui et al. in U.S. Pat. No. 4,125,362, issued Nov. 14, 1978, teach that RTV silicone rubbers which contain from 25 to 35 weight percent non-reactive dimethyl silicone oil can produce more copies before the offset phenomenon or sheet sticking phenomenon are observed. The RTV silicone rubber contains fumed silica, diatomaceous earth, and ground quartz filler. The RTV silicone rubbers containing 25 to 35 weight percent non-reactive silicone oil produce no less than 20,000 copies before the offset and sticking phenomenon are observed, whereas RTV silicone rubber containing more or less of the silicone oil than the 25 to 35 weight percent produce only between 5,000 and 10,000 copies before one of the phenomenon is observed.
Other patents relating to heat fixing rolls using silicone rubber outer layer and also discussing the use of fillers therein include U.S. Pat. No. 3,795,033, issued Mar. 5, 1974, to Donnelly et al. and U.S. Pat. No. 4,075,390, issued Feb. 21, 1978, to Murphy.
Namiki in U.S. Pat. No. 4,019,024, issued Apr. 19, 1977, teaches room temperature-vulcanizable silicone rubber containing 4 to 40% silicone oil of low viscosity to make the periphery layer of silicone rubber. Namiki also teaches that silicone rubber has poor adhesiveness to the core material and the core surface is preferably primed with a silicone varnish, silane coupling agent, or a silicone rubber.
Takamizawa et al. in U.S. Pat. No. 4,057,596, issued Nov. 8, 1977, teach silicone rubber compositions suggested as useful coating technology in which the techniques of offset printing are used because the compositions have low viscosities, such as below 10,000 centistokes (0.01 m.sup.2 /s). These compositions are described as comprising vinyldimethylsilyl terminated diorganopolysiloxane, a hydrogendimethylsilyl terminated diorganopolysiloxane, a methylvinylpolysiloxane having at least three vinyl groups, a methylhydrogenpolysiloxane having at least three hydrogen atoms bonded directly to the silicon atoms, a catalyst for the addition of silicon-bonded vinyl groups and silicon-bonded hydrogen atoms. The catalyst includes platinum catalyst. Also the use of retarding agents for platinum catalysts is described as optional.
Takiguchi et al. in U.S. Pat. No. 4,064,313, issued Dec. 20, 1977, teach adhering the silicone rubber outer layer to the base member (core substrate) by using a novel polysiloxane composition. Primers for adhering the outer layer to core substrates are also taught by Takiguichi et al. in U.S. Pat. No. 4,078,286, which patent also identifies silicone rubbers at RTV, LTV, or HTV types.
Other patents which describe heat fixing rolls with a silicone rubber outer layer include U.S. Pat. No. 4,099,312, issued July 11, 1978, to Hill et al.; U.S. Pat. No. 4,188,423, issued Feb. 12, 1980, to Swift; and U.S. Pat. No. 4,254,733, issued Mar. 10, 1981, to Namiki.